This invention relates to nuclear reactors and has particular relationship to the replacement of old split-pin assemblies of a guide tube of a nuclear reactor with new split-pin assemblies. According to the teachings of Calfo the old split-pin assembly, secured in the upper and lower counterbores of the lower circular flange of the lower guide tube (LGT) of the reactor, is processed in a pool of borated water in a work station which includes a plurality of robotic tools. Each guide tube is equipped with two split-pin assemblies located in the lower flange 180.degree. apart. The LGT is precisely positioned by a clamp-and-index tool. The old split-pin assembly is then severed by a metal-disintegration machine tool predominantly into two fragments; one fragment (herein referred to as the "nut fragment") consists of the residual part of the old nut and part of the old split pin threaded to it, and the other consists of the residual part of the split pin. The latter is extracted from the lower counterbore of the flange and deposited in a trash chute by a pin puller and expeller on the clamp-and-index tool. At this point it becomes necessary to remove the nut fragment from the upper counterbore of the flange and then to secure the new split-pin assembly in this flange. A difficulty which is imposed in carrying out this phase of the replacement is that the new nut is only partially accessible for mechanical processing. The nut extends from the upper counterbore into a slot in a wall of the LGT which has the shape of, and is referred to as, a "mousehole". Only a limited area external to the "mousehole" is accessible for removal of the nut fragment and for insertion in the upper counterbore of a new nut and threading it to a new pin. In addition, the tines (or leaves) of the pins must be properly aligned with respect to the top flange of the guide tube. This invention concerns itself with the phase of the overall replacement operation involving the removal of the old nut fragment and its replacement by a new nut in the flange of the LGT.
It is an object of this invention to provide apparatus for removing the nut fragments from the upper counterbore of the flange, and, after the upper and lower counterbores have been cleaned, to replace the old nut fragment by a new nut in the flange without damage to the LGT.
The replacement is carried out in two stages. In the first stage the nut fragment is removed from the upper counterbore and is replaced by a new nut. The conditions imposed on the tooling and the practice for accomplishing this purpose is as follows:
1. It must be capable of operation within the space confines imposed by, and in cooperation with, the other tooling in the robotic work station. PA1 2. It must be capable of operation in the limited space available external to the "mousehole". PA1 3. There must be accessibility for supplying new nuts from the deck above the pool. PA1 4. The tooling and practice must be capable of operation, when coupled with a programmable computer, in an automatic mode. PA1 5. The tooling must be capable of operating in borated water. PA1 0.degree. position--sever old split-pin assembly and dispose of pin fragment, PA1 180.degree. position--remove and dispose of nut fragment, PA1 0.degree. position--clean counterbores, PA1 180.degree. position--insert new nut, PA1 180.degree. position--insert new pin, torque nut to pin. PA1 1. Moves inwardly toward the guide tube from its "home" (storage) position to an advanced position where it is stopped by a preset stop. PA1 2. Rotates typically approximately 90.degree. to position the jaws of the clamp about the old nut fragment. An adjustable stop, which acts against the guide tube flange, is provided to assure that the jaws are properly positioned with respect to the nut. PA1 3. Clamps the old nut fragment. PA1 4. Lifts the fragment from the upper counterbore. PA1 5. Rotates back to the advanced position, typically about 90.degree. (reverse of step 2). PA1 6. Moves back to its "home" position (reverse of Step 1). This motion is also arrested by an adjustable stop which is preset to locate the nut directly over a trash chute which guides the nut fragment to a disposal basket; the stop also positions the clamp to engage a new nut fragment in the unloading port of the hopper. PA1 7. The nut is lowered (reverse of Step 4). PA1 8. The nut is unclamped (reverse of Step 3), thus, allowing it to drop into the chute. PA1 1. While located in its "home" position, the clamp is rotated against the nut hopper. The adjustable preset stop which properly locates the jaws of the clamp with respect tot he nut fragment in the guide tube, also locates these jaws with respect to the new nut in the hopper. PA1 2. Clamps the new nut. PA1 3. lifts the new nut from the hopper. PA1 4. Rotates back to home position (reverse of Step 1). PA1 5. Moves toward LGT (Step 1 of nut removal). PA1 6. Rotates 90.degree. to position the new nut above the LGT upper counterbore (Step 2 of nut removal). PA1 7. Lowers the nut into the counterbore (reverse of Step 3). PA1 8. Unclamps the nut (reverse of Step 2). PA1 9. Rotates back 90.degree. (reverse of Step 6). PA1 10. Returns to "home" position (reverse of Step 5). PA1 1. By changing the sequence of operations, the tool can perform the two required operations. PA1 2. The tool is capable of being operated automatically when coupled with a programmable computer (see Calfo). PA1 3. The tool is capable of operating manually and when operated in a manual mode, the tool can correct undesired abnormalities which may arise during the course of operation. PA1 4. The tool is capable of being aligned prior to its disposition in the pool. PA1 5. The tool can be operated remotely when submerged in the borated water of a reactor pool. PA1 6. The tool is composed of stainless steel and is resistant to the borated water.
In the second stage the new split pin is inserted in the new nut and the new split-pin assembly is secured to the flange by threading and properly torquing the new nut onto a new split pin. This invention concerns itself only with the first stage.
It is an object of this invention to provide tooling which shall meet the above conditions for removing the nut fragment and installing new split-pin assemblies in the lower flange of a LGT of a reactor without damage to the LGT.